This invention relates to pressure measuring and monitoring devices. In particular, it relates to devices for continuously and precisely measuring pressure within a confined and relatively inaccessible space such as, but not by way of limitation, the intracranial pressure of a living human being, as exemplified in U.S. Pat. Nos. 3,686,958 and 3,789,667, whose disclosures are incorporated herein by reference, or the arterial or venous blood pressure of a living human being, or the like.
In the devices of the above mentioned patents a plurality of light guides is introduced through a pneumatic line to the interior of a flattened envelope having flexible side walls. In the U.S. Pat. No. 3,686,958 a pair of light guides is employed, one input and one output, having their internal ends facing each other and a shutter is movable by movement of a flexible side wall to modulate passage of light from one light guide end to the other with changes of relative pressure inside and outside the envelope. In the U.S. Pat. No. 3,789,667 three side by side light guides are employed, one for input of light and two for output. A reflector mounted on a side wall is arranged opposite the three internal light guide ends and moves, with movement of the side wall, in a plane parallel to the end faces of the guide so as differentially to reflect light from the input guide to the output guides. External apparatus senses the light intensities of the outputs of the output guides and, through the pneumatic line, varies the pressure in the envelope to equal that which surrounds it while at the same time displaying the pressure for monitoring purposes.
I have found that the flattened envelope configuration severely limits the minimum size of the pressure detector unit, correspondingly limiting the number of different pressure measuring and monitoring applications to which it can be put, and that sensitivity can be improved by eliminating actuation of the light modulating element by a flattened side wall and employing a new and improved arrangement and mode of operation for the differential reflection of light from the inner end of an input guide to the inner ends of two output guides.